Loop antenna



Jan. 10, 1950 R. A. MORRIS ETAL 2,494,255

LOOP ANTENNA Filed Dec. 20, 1945 SYNTHt'T/C memo Alumna/10ml CO TTONCONDUCTOR INSULATING TH/PfAD fivezzfara Fa /1220124! vhf/70nd? fa e/2%01. [person Patented J an. 10, 1950 u NITED STATE s PATENT OFFICE LOOPANTENNA Raymond. A. Morris and Frank AQIVerson, Chicago, 111., assignorsto Edwin I. Guthman & '00., Inc., Chicago, 111., a corporation ofIllinois Application December 20, 1945, SerialNo. 636,240-

.This invention relates to a loop antenna and wire for'r'naking a loopantenna or the like. Loop antennas for small radio receivers have beenformed by winding wire to provide a flat pancake structure. In order fora loop antenna to operate properly, it must have certainphysicaldimensions and preferably have a certain capacitance and low losscharacteristics. The necessity for having low distributed capacitance ina loop antenna makes it necessary to provide adequate spacing betweenwire turns. It is desirable that such spacing between wire turns have aminimum solid insulating material to reduce the dielectric losses.

In accordance with this invention, a loop antenna is provided having asimple construction in which most of the insulating medium betweenadjacent wire turns consists of air. At the same time, however, theconstruction is relatively rigid, easy to manufacture, and thoroughlypractical.

I The wire of which the loop antenna is formed is provided with aninsulating material having such a shape and dimension as to providemaximum spacing between adjacent wire turns with minimum insulatingmaterial. It is clear, therefore, that wire embodying this invention maybe used for other purposes than loop antennas. Thus,

in certain types of radio frequency transformers and chokes, it isnecessary to reduce dielectric losses and distributed capacitance. Awire embodying the present invention may be used in the manufacture ofsuch coils.

In its more general form, the invention provides for the use of barecopper or other wire upon which is wound a coarse spiral of insulatingmaterial. This insulating material may be a coarse filamentary thread ofsuitable material having a sufficiently large diameter to define asubstantial region around the wire. The insulating material may bepartly or completely of synthetic material such as cellulose acetate,nylon, rayon or other textile material. The presence in part at least ofa synthetic textile material is preferred for the reason that cheapsolvents therefor are readily available. Thus, two adjacent lengths ofwire insulated as indicated may be cemented together by the use of atextile material solvent. However, conventional material, such as cottonor silk, may also be used.

Instead of a solvent for the insulating material, such materials as glueor cement may also be used.

For a fuller description of the invention, reference will now be made tothe drawings wherein 4 claims (01. 250'33.67) 7 Figure 1 is a top planview of a loop antenna embodying the present invention.

Figure 2 is a detail of the insulating thread.

in accordance with the present invention;

R e ferring specifically to the drawings, in Fig- .UI B 3;,wireHlissh'own as wound with a filamentary insulating thread ll. Wire I0 isshown as a solid Wire. However, stranded wire may be used if desired.While wire In may be conventionally insulated, it is preferred to usebare wire.

Filamentary thread ll may have any desired diameter, preferably of theorder of that of wire [0, and the winding pitch may be as great or assmall as may be found convenient. Filamentary thread ll may be attachedto wire l0 by the use of any suitable material such as rubber cement, asolution of cellulose acetate, or the like. this fashion, a strong bondbetween thread i I and wire It] may be obtained.

Thread II, as previously stated, may be of any suitable textilematerial. Thus, it may be entirely of cotton or entirely of somesynthetic textile material as cellulose acetate or any of the othermaterials previously mentioned or a combination of these.

Inasmuch as synthetic fibers are generally more expensive than cotton,thread ll may be formed of two threads I2 and I3 twisted around to forma single composite thread. Thread l2 may be of cotton, while thread [3may be of cellulose acetate; As shown, thread I3 is wound around threadl2. The pitch may be as coarse as desired.

The advantage of using a composite thread, as shown in Figure 2, is thatthe acetate thread may be affected by solvents as acetone, for example,readily available on the market. While. solvents are available forcotton, as a rule they are expensive and undesirable to use. Thus, thesynthetic thread is distributed around in the composite thread so thatbonding of the entire composite thread may be easily effected. It isobvious that other types of composite thread may be used.

Thus, the two threads may be simply twisted or a simple cotton threadmay have its outer surface chemically treated or may have a celluloseacetate coating precipitated over it.

A loop antena made of the wire shown in Figure 3 is shown in Figure 1.This consists of a plurality of turns I5 of wire to form a flat annularcoil. Leads 16 and I! are provided for connection to a radio receiver.As clearly indicated in Figure 1, the relatively coarse insulating Bytreating the insulated wire in thread ll imparts a desirable spacefactor to adjacent wire turns. The loop antenna itself may be formed inany desired fashion and, after formation, may be dipped into anysuitable cement or solvent. Instead of dipping into the solvent orcement, the loop may be sprayed. In any event, it is preferred to use aslittle cement or solvent as possible. By using a solvent with a lowsurface tension, and most textile solvents are of that character, thespaces between the wire will remain substantially free of solidmaterial.

What is claimed is:

1. A loop antenna comprising a plurality of turns of wire, said wireconsisting of a conductor having insulating material wound around thewire to form a helix with the pitch of said helix being coarse enough toexpose most of the wire surface to the atmosphere, adjacent wire turnsbeing maintained in predetermined spaced relation by cement on saidinsulating material with the spacing between wire being controlledsubstantially solely by the thickness of the insulating material.

2. The antenna of claim 1 wherein said insulating material is a textilethread.

3. The loop antenna of claim 1 wherein said insulating material is athread consisting oi cot- REFERENCES CITED The following references areof record in the tile; of this patent:

UNITED STATES PATENTS Number Name Date 1,553,315 Gould Sept. 15, 19251,601,817 Forster Oct. 5, 1926 2,018,477 Wentz Oct. 22, 1.935 2,030,1 0Titcomb Feb. 11, 1936 2,197,616 Lehne et a1 Apr. 16, 1940 FOREIGNPATENTS Number Country Date 529,892 Germany July 18, 1931

